This invention relates to a process for controlling the cloud point of transportation fuels including diesel fuel and aviation fuel from renewable feedstocks such as the glycerides and free fatty acids found in materials such as plant oils, fish oils, animal fats, and greases. The process involves hydrogenation, decarboxylation, decarbonylation, and/or hydrodeoxygenation and hydroisomerization in two or more steps. Desired product specifications and yields are determined and recycle streams are set to achieve the specifications and yields.
As the demand for transportation fuel increases worldwide there is increasing interest in sources other than petroleum crude oil for producing diesel and aviation fuel. One such source is what has been termed renewable feedstocks. These renewable feedstocks include examples such as plant oils such as corn, rapeseed, canola, soybean and algal oils, animal fats and oils such as tallow, fish oils and various waste streams such as yellow and brown greases and sewage sludge. The common feature of these feedstocks is that they are composed of glycerides and Free Fatty Acids (FFA). Both of these types of compounds contain aliphatic carbon chains generally having from about 8 to about 24 carbon atoms. The aliphatic carbon chains in the glycerides or FFAs can be saturated or mono-, di- or poly-unsaturated. Most of the glycerides in the renewable fed stocks will be triglycerides, but some of the glycerides in the renewable feedstock may be monoglycerides or diglycerides. The monoglycerides and diglycerides can be processed along with the triglycerides.
There are reports in the art disclosing the production of hydrocarbons from plant oils. For example, U.S. Pat. No. 4,300,009 discloses the use of crystalline aluminosilicate zeolites to convert plant oils such as corn oil to hydrocarbons such as gasoline and chemicals such as para-xylene. U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon products in the diesel boiling range by hydroprocessing vegetable oils such as canola or sunflower oil. Finally, US 2004/0230085 A1 discloses a process for treating a hydrocarbon component of biological origin by hydrodeoxygenation followed by isomerization.
The process herein comprises an optional pretreatment step, and one or more steps to hydrogenate, deoxygenate, hydroisomerize and selectively hydrocrack the renewable feedstock, to generate at least a diesel fuel component and optionally, an aviation fuel component. The specifications and relative yields of the diesel component and the aviation component are determined and the amount and type of recycle to the isomerization and selective hydrocracking zone is determined in order to meet the specifications and yields of the products. The diesel component and the aviation component may be suitable as fuels, used as components in blending pools, or may have one or more additives incorporated before being used as fuels.